JPH04313110A - Voltage follower circuit for power-level control circuit - Google Patents

Abstract

PURPOSE: To obtain the voltage follower circuit for control over the power level of a power control system. CONSTITUTION: The voltage follower circuit 17 is inserted between a load power control circuit 19 which adjusts the level of electric power supplied to a load and variable impedance 10 having internal impedance determining a desired level of the electric power. The feedback voltage from the output of the voltage follower circuit 17 is compared with a corresponding voltage across the variable impedance and the difference between those voltages is used to drive the output voltage of the voltage follower circuit to follow up the input voltage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to voltage follower circuits, and more particularly to voltage follower circuits for power level control.

0002

BACKGROUND OF THE INVENTION For certain electrical devices, it is advantageous to have the ability to control or adjust the level of power provided. In these electrical devices, the user can achieve this control by adjusting elements in the circuit, such as potentiometers, through the functionality of a circuit commonly referred to as a load power control circuit.

[0003] There are many situations in which such control as described above is necessary. For example, in some applications it is desirable to be able to manually control the level of illumination provided by fluorescent lighting. In modern types of such dimmable fluorescent lighting systems, power is supplied to the individual fixtures through circuits called electronic ballasts, which function as the load power control circuits described above within the fluorescent lighting fixtures. In the design of commercially available systems, the dimming level (dimming level)
is adjusted by changing the value of an external variable control impedance connected between a pair of control terminals (ballast control terminals) of the electronic ballast. The electronic ballast includes a current source connected in parallel with a resistor between a pair of ballast control terminals. By changing the control impedance between the ballast control terminals, a dimming control signal voltage is generated between these control terminals, which is detected by other elements in the internal circuit group of the electronic ballast, and when the electronic ballast is equipped. The illumination level generated by the fixture changes in response to this control signal. The control voltage across the ballast control terminals is approximately 1 at minimum illuminance.
volts to about 10 volts at full illumination. Each electronic ballast provides power to a pair of fluorescent bulbs.

It is also possible to connect a number of individual ballast control terminals to a single controlled impedance circuit by grouping the ballast control terminals between the terminals of the controlled impedance circuit. In this commercial product design, the controlled impedance circuit includes a semiconductor active element that makes the control characteristics of the impedance circuit, which is a function of the resistance of the adjustment potentiometer, largely independent of the number of electronic ballasts controlled by the impedance circuit. are doing. That is, the illumination level of an individual fixture will be approximately the same level for any fixture for a given mechanical position of the regulating element of the controlled impedance circuit, regardless of the number of impedance-controlled electronic ballasts.

This controlled impedance circuit consists of six individual
It has the ability to control dimming for as many as 0 electronic ballasts. The number of ballasts that a single controlled impedance can control is directly related to the impedance's ability to absorb the current that each individual electronic ballast produces at its respective control terminal.

In some applications, the design specification of 60
It is advantageous to be able to control more than one instrument with one impedance. Although 60 fixtures may seem like a lot, many commercial and office buildings have literally hundreds of fluorescent light fixtures installed, and it is difficult to control these fixtures with a single control element. Sometimes things are desirable. In order to have a control impedance capable of controlling more than 60 electronic ballasts, a built-in power supply is required, which increases manufacturing and installation costs. Therefore, there is a demand for the development of some means to avoid these restrictions. In particular, it would be extremely useful if a means were developed to transparently interface between a single controlled impedance and multiple fluorescent lighting fixtures.

There is a wealth of literature regarding regulating the amount of power delivered to a load. In the field of light dimmer control, which is particularly relevant to the present application, U.S. Pat. An optical circuit is disclosed. Others: U.S. Patent No. 4,645,979, No. 4,651,060, No. 4,686,427, No. 4
, 704,563, 4,712,045, and 4,717,863 also disclose dimming circuits for fluorescent lamps.

It is believed that a consideration of certain aspects of equivalent circuit theory will be helpful in understanding the following description of the invention. The concept of a current source is well known to those skilled in the field of electronics, and in fact, in commercial products of electronic ballasts as described above, a current source connected in parallel with a resistor is used as the power source at the input terminals. ing. It is well known that, instead of a voltage source in series with a resistor, equivalent electrical characteristics can be obtained by using a current source in parallel with a resistor of a different value. Therefore, in this discussion, consideration should be given below to a current source connected in parallel with a resistor of a certain value, which can be interchanged with a voltage source connected in series with a resistor. In particular, when the term "voltage source" is used in this application, it is not meant to limit the disclosure related thereto to that particular embodiment, but also includes current sources equivalent to the voltage source. It should be understood that

[0009]

[Means for Solving the Problem] As mentioned above, in a certain power control system, the power level is adjusted by adjusting the external impedance between the control terminals of the load power control circuit that operates to adjust the power to the load. controlled by The present invention particularly relates to a system configured to vary the power supplied to a fluorescent lamp fixture to vary the illuminance of the fixture, and which includes an electronic ballast comprising a load power control circuit. These load power control circuits supply a voltage to the control terminals that changes depending on the value of the variable control impedance between the control terminals. The present invention
A voltage follower circuit is inserted between the variable control impedance and the plurality of load power control circuits, and reproduces the state of the output terminal of the variable control impedance to the control terminal of the load power control circuit.

[0010] Such a voltage follower circuit has a pair of input terminals to which a variable control impedance can be connected, and a plurality of individual loads can be controlled by a single variable control impedance with almost no change in control characteristics. A pair of output terminals are provided to which the control terminals of the plurality of load power control circuits can be connected together. In a broad sense, the voltage follower circuit of the present application includes: a voltage source; a resistor connected in series with the voltage source between input terminals of the voltage follower circuit; an output terminal forming an output terminal of the voltage follower circuit; a variable output impedance having an input terminal for controlling impedance between the terminals; the output impedance increases as the voltage at the input terminal decreases; and the output impedance decreases as the voltage at the input terminal increases; It was designed to do so. Further, the voltage between the output terminals of the variable output impedance is inputted as a first input, and the voltage between the input terminals of the voltage follower circuit is inputted as a second input, and the voltage between the first input and the second input terminal is inputted to the input terminal of the variable impedance. Voltage detection means are provided for providing an output signal representative of the voltage difference with the input. By feedback of the voltage between the output terminals of the variable output impedance, the voltage detection means can drive the variable output impedance to accurately follow the voltage at the input terminal of the voltage follower circuit.

In particular, it is an object of the invention to be able to drive a very large number of loads and change the power input of all of them simultaneously by the same amount. With regard to the uses of the present invention, there are literally thousands of
It is useful for controlling the power input of large lighting installations with as many as 0 luminaires with a single controlled impedance.

Other objects and advantages of the invention will become apparent from the following description of the embodiments.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a circuit that performs on/off operations and power adjustment for a load. The user of the load can adjust the power and turn it on/off by appropriately setting the variable control impedance 10. In FIG. 1, the variable controlled impedance 10 is depicted as a simple variable resistor, but in actual commercial product implementations, circuits including semiconductor active components are used, and the detailed configuration of the variable controlled impedance is shown in FIG. is irrelevant to the present invention. Power for these active semiconductor components is input to control terminals (control input terminals) 11 and 12 from a DC (direct current) voltage source 15 in series with a resistor 14 .

In FIG. 1, the on/off and power level control functions are illustrated as being performed by separate elements, with the on/off function being performed by voltage sensor 16 and switch 18. When switch 18 is closed, a current flows between switch terminal 24 and switch terminal 25, and the current flows through load power control circuit 19 and terminals 22 and 2.
3 to the load. The power control function is performed by a voltage follower circuit 17 that provides a control signal via lead 27 to a load power control circuit 19 . In embodiments of the invention relating to fluorescent lighting control, the load power control circuit 19 comprises the electronic ballast described above.

In the design of the commercial product embodiment, a voltage source 15, a resistor 14, a voltage sensor 16 and a switch 18 are used.
, it is advantageous to combine the voltage follower circuit 17 into a single modular unit 1 so that the power supplied to the load can be adjusted and opened and closed under the control of the variable impedance 10 only.

Switch 18, under control of voltage sensor 16, disconnects the load from power input terminals 20 and 21 in response to the voltage between terminals 11 and 12 dropping within a preselected range, and controls the When the voltage between terminals 11 and 12 is outside the above range, the load is connected to power input terminals 20 and 21. In this embodiment of the invention, the preselected voltage range is from 0.1 to about 0.5 volts. When the voltage between terminals 11 and 12 is between 0 and 0.5 volts, voltage sensor 16 provides a signal voltage at terminal 26 and switch 18 responds by opening the connection between terminals 24 and 25. . The voltage between control terminals 11 and 12 is approximately 0
．． 8 volts or more, switch 18 connects terminals 24 and 2.
5 is electrically connected. In the range of 0.5 to 0.8 volts, the state of switch 18 does not change.

The voltage developed at terminal 27 of voltage follower circuit 17 in this embodiment closely follows or mirrors the voltage between terminals 11 and 12 of variable control impedance 10. In addition, such an input interface for the voltage follower circuit 17 is made compatible with the interface of the load power control circuit 19, so that commercially available products with the same variable control impedance 10 can be interchangeably connected to either input terminal. It is desirable to be able to do so. The input interface for the load power control circuit 19 includes a DC current source and a parallel resistor. Resistor 1
4 and the voltage source 15 in series with it, the input interface of the voltage follower circuit 17 is connected to the load power control circuit 19.
is selected to match the input of Preferably, the design of the voltage follower circuit 17 is such that a significant number of voltage follower circuits can be connected together to the variable impedance 10 at the input or control terminals 11 and 12. This design allows more load control circuits 19 to be controlled by a single variable control impedance 10 than without the voltage follower circuit 17. Furthermore, the input interface for the voltage follower circuit 17 is made compatible with the input of the load power control circuit 19, and these two types of circuits are connected to the variable impedance 10 in a mixed manner at the input terminals of these circuits. It is desirable to be able to do so.

According to the voltage follower circuit 17 of this embodiment, as many as 10 voltage follower circuits 17 can be driven with a commercially available variable control impedance. As many as 600 load power control circuits 19 can be controlled by a single variable control impedance 10, compared to 60 that can be controlled by a single variable control impedance 10 without using the circuit 17.

According to the power adjustment voltage follower circuit 17 and the load power control circuit 19, the power supplied to the load can be adjusted. Again, the impedance between control terminals 11 and 12, measured by sensing the voltage between these terminals, controls the level of power delivered to the load. The design of the voltage follower circuit 17 and load power control circuit 19 is such that the power delivered to the load is maximum when the voltage between control terminals 11 and 12 is maximum, and as the voltage and impedance between these terminals decreases, the power delivered to the load increases. The amount of electricity supplied to the area is also decreasing.

The assembly of the individual circuit components of the three block elements voltage sensor 16, voltage follower 17 and switch 18 into a single modular unit 1 is shown in FIG. In FIG. 2, DC voltage source 15 is connected to terminals 20 and 21.
The transformer 15b is powered by a transformer 15b which supplies a 15 volt AC output to a full wave rectifier 15a. The output of full wave rectifier 15a is supplied to filter/regulator element 15d via coupling diode 15c. The output of filter/regulator element 15d is 12v
DC and supplied to the resistor 14 for control signals, and
It is supplied to operational amplifiers 35 and 44 as power. Filter/regulator 15d from full wave rectifier 15a
The DC output before passing through is used for certain operations of the switch element 18.

In the following discussion including both operational amplifiers 35 and 44, it is assumed for convenience that these operational amplifiers are high gain voltage amplifiers with differential inputs. The term differential input means that a variable or control voltage can be input to either or both of the + and - terminals. The output of each operational amplifier 35 and 44 is a voltage that is a large multiple of the voltage difference between the positive and negative input terminals, for example several hundred to several thousand times as large. When the - terminal voltage exceeds the + terminal voltage, the output is simply driven to 0 volts (ground). Because the voltage amplification is large and the output voltage can never exceed the input voltage applied to these amplifiers,
The range of input voltage differences that exist between the output limits of 0 volts and 12 volts is relatively narrow.

The voltage at terminal 11 is supplied to the negative input terminal of operational amplifier 44 via resistor 51. operational amplifier 4
A feedback voltage is supplied to the + input terminal of No. 4 through a resistor 43. The source of this feedback voltage will be explained later. The output of the operational amplifier 44 is
Applied to a voltage divider circuit consisting of resistors 45 and 46. The voltage between these two resistors 45 and 46, the collector of transistor 47 and the terminal 27 is the voltage of transistor 4
Applied to the base of 7. Transistor 47 functions as a variable impedance that keeps its collector voltage very close to the voltage at terminal 11. transistor 47
The collector voltage of is the feedback voltage supplied to the + input terminal of the operational amplifier 44 mentioned above. operational amplifier 4
A capacitor 52 connected between the positive input terminal and the output terminal of the operational amplifier 44 provides stability to the output of the operational amplifier 44. As the collector voltage of transistor 47 increases for a given voltage at control terminal 11, transistor 47 conducts more strongly and the collector voltage drops. It can therefore be seen that the voltage at the collector of transistor 47 and at terminal 27 will always be several millivolts higher than the voltage at input terminal 11 applied to the - input terminal of operational amplifier 44. In this way, the operation of the load power control circuit 19 when driven by the voltage follower circuit 17 is controlled by the control terminals 11 and 12.
(ground) with a variable controlled impedance connected between
From there, terminals 27 and 64 of the load power control circuit 19
It can be seen that the operation is essentially the same as if it were moved to a (ground) voltage follower output connection. Zener diode 41 and capacitor 42 provide protection against electrostatic voltage surges at the output of the voltage follower circuit in the same way that Zener diode 48 and capacitor 49 provide input protection at the control input.

Current source 55 and resistor 56 power the variable controlled impedance. The variable control impedance is connected between input terminals 11 and 12 in the present invention, rather than being connected to terminal 27 as is conventional. Current source 55 and resistor 56 together with power converter 62 form load power control circuit 19 shown in FIG. According to this configuration of the voltage follower circuit 17, complete compatibility (compatibility) between the output of the voltage follower circuit 17 and the input of the voltage control circuit 19 can be ensured.

ON/OFF CONTROL Turning first to switch element 18, a voltage divider consisting of resistors 30 and 31 is connected between the output of filter/regulator element 15d and ground. The values of resistors 30 and 31 are approximately 0.
5v is selected to appear. The voltage generated at the connection point between resistors 30 and 31 is applied to the + input terminal of operational amplifier 35.

The voltage at the control terminal 11 is supplied to the negative input terminal of the operational amplifier 35 via a resistor 51. The role of the resistor 51 is simply to attenuate the discharge of static charges that may occur on the terminal 11. The value of resistor 51 is the same as that of operational amplifier 3.
much smaller than the input impedance of 5, 10,0
Since the resistance is only about 0.00 ohms, it has almost no effect on the response of the operational amplifier.

The voltage between control input terminals 11 and 12 is provided via resistor 14 by the output of filter/regulator element 15d. Therefore, control input terminals 11 and 1
It can be seen that if the variable controlled impedance 10 between 2 changes, the voltage at the terminal 11 changes, that is, if the value of the controlled impedance increases, this voltage also increases, and if the value of the controlled impedance decreases, it decreases. The role of Zener diode 48 and capacitor 49 is to protect against electrostatic charge discharge that could damage the semiconductor components within arithmetic multipliers 35 and 44.

The output of the operational amplifier 35 is supplied to a pair of resistors 33 and 34 connected in series. Resistor 33 limits the flow of current from operational amplifier 35, while these two series connected resistors provide a voltage to ensure that transistor 36 is cut off when the output of operational amplifier 35 goes low. It also functions as a divider. The feedback resistor 32 connects the output of the operational amplifier 35 to the operational amplifier 3.
Connect to the + input terminal of 5. The purpose of the resistor 32 is to create a dead zone to stabilize the response of the operational amplifier 35.
The voltage at the - terminal is only slightly smaller than the voltage at the + terminal (approximately 0).
．． (within 3v) If it is not negative, the purpose is not to change the output of the operational amplifier 35.

The voltage output at the junction between resistors 33 and 34 is provided to the base of NPN transistor 36. The emitter of the transistor 36 is grounded, and the collector is connected to the coil 37 of the first relay. The first relay is
It has a normally closed contact 38 controlled by a winding 37 which is connected to the winding 3 when the transistor 36 is cut off.
When no current flows through 7, it becomes conductive. The output from the full-wave rectifier 15a, before passing through the filter/regulator 15d, is supplied via a contact 38 to a terminal 26 and thence to a second relay winding 18a forming the switch 18 described in FIG. Winding 18a connects terminals 24 and 25
Controls the normally open contact 18b connected between. As is clear from the figure, when contact 18b closes, terminals 20 and 2
1 is supplied to load terminals 22 and 23 via the illustrated power converter element 62.

The circuit operation is controlled by the value of the impedance connected between control input terminals 11 and 12. In this embodiment, the 12V voltage applied to terminal 11 via resistor 14 is dropped by variable controlled impedance 10 from a maximum of 10V to a minimum of 0.1 to 0.
The voltage changes between up to 2V. When the voltage at terminal 11 exceeds 0.5v which is supplied to the + input terminal of operational amplifier 35, operational amplifier 3 which is supplied to resistors 33 and 34
The output of transistor 5 becomes approximately 0V, and the base voltage of transistor 36 also becomes 0V. The base voltage of transistor 36 is 0
When the voltage reaches V, the transistor 36 is cut off, so no current flows between the collector and the emitter, and therefore no current flows through the winding 37 of the first relay. Therefore, the contact 38 is closed and current flows through the winding 18a, thereby keeping the contact 18b closed. In this way,
Power is supplied to load terminals 22 and 23 via a power converter 62.

When the voltage at the control input terminal 11 is lower than 0.5v, the output of the operational amplifier 35 will be about 10v. Current supplied through resistor 33 to the base of transistor 36 drives transistor 36 into a conductive state. When transistor 36 conducts, winding 37 causes contacts 38 to open and become non-conductive. When the contact 38 becomes non-conductive, current does not flow from the terminal 26 to the winding 18a, and the contact 18
b opens and connects load terminals 22 and 23 to power supply terminals 20 and 2.
Separate from 1. Connect variable control impedance 10 to terminal 1
Setting the voltage between 1 and 12 to a value that reduces it below 0.5v effectively acts as if impedance 10 were in the off position.

The transistor 47 operates to cut off the contact 18.
When a opens, the induced surge caused by the degeneracy of the magnetic fields in relay windings 37 and 18a can create an excessive voltage between transistor 47 and the emitter and collector. Considering damage caused by such surges, winding 3
It is desirable to connect a diode (not shown) across transistor 47 and contact 18a to dissipate surges and prevent damage to transistor 47 and contact 38. Measures of this kind are well known.

As mentioned in FIG. 1, contact 18b
It is important to provide a certain range between the voltage between the terminals 11 and 12 at which the contact 18b opens and the voltage at which the contact 18b closes and becomes conductive. This range setting is a function of the feedback resistor 32 and the dead band created thereby. When the voltage at the - input terminal of operational amplifier 35 drops below 0.5v, its output voltage rises to about 10v. The value of the resistor 32 is such that the + input terminal of the operational amplifier 35 is connected to approximately 0.8V.
is selected to be large enough to pull up to . When the value of variable control impedance 10 increases and the voltage between terminals 11 and 12 increases with it, operational amplifier 35
must reach a level of 0.8 volts before its output voltage drops to about 0.5 volts, causing transistor 36 to cut off and contact 18b to close. Therefore, when the voltage at the - input terminal of the operational amplifier 35 is low, the resistor 32 pulls up the voltage at the + input terminal by several tenths of 1 volt, and when the output of the operational amplifier 35 is low, + Pulls down the voltage of the input terminal. Therefore, resistor 32 increases stability and provides variable controlled impedance 10
Normal variations in the voltage between terminals 11 and 12 due to variations in the supply voltage or variable control impedance 10 trigger operational amplifier 35 to switch the output, in addition to changes in the voltage at terminal 11 due to manual adjustment of to prevent

In the two circuits described above, components with the following values and names are preferably used:

Resistor 14, 40, 34, 46, 61 4, 70
0Ω rectifier 15a
Diode 15c consists of 1N4004 type diode
1N4004 type resistor 30
240,00
0Ω resistor 31, 33, 45, 43, 51 10
,000Ω resistor 32
1,000,000Ω operational amplifier 35, 44
LM358N type transistor 36, 47
2N3904 type capacitor 42,
48,52 0.1mfd. Zener diode 41, 48 1N4
740A type 10v, 1w 1st relay
Arom
at Corp. Made
VC2
0-1A-DC12V type 2nd relay
Aromat
Corp. Made
HD1E-
M-DC12V

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit that integrates power control and on/off control of a load such as a lighting fixture.

FIG. 2 is a circuit diagram showing in detail the on/off function and power adjustment function portion of the block diagram of FIG. 1;

[Explanation of symbols]

10 Variable control impedance 11, 12 Control input terminal 14 Resistor 15 DC voltage source 16 Voltage sensor 17 Voltage follower circuit 18 Switch 19 Load power control circuit 20, 21 Power input terminal 35, 44 Operational amplifier 55 Current source

Claims (1)

[Claims] 1. A load power control circuit that changes the level of power supplied from a power supply to a load according to the value of a variable control impedance supplied between control terminals, the control terminal having the variable control impedance connected to the control terminal. a load power control circuit configured to supply a voltage that changes according to the value of;
a pair of input terminals between which the variable control impedance can be connected, and a plurality of the loads so that the plurality of individual loads can be controlled by a single variable control impedance with almost no change in control characteristics. and a voltage follower circuit having a pair of output terminals to which control terminals of the power control circuit can be connected, wherein: a) a voltage source; b) a voltage between the input terminals of the voltage follower circuit; a resistor connected in series with the source; c) an output terminal forming an output terminal of the voltage follower circuit;
and a variable output impedance having an input terminal for controlling the impedance between the output terminals, the variable output impedance increasing as the input terminal voltage decreases and decreasing as the input terminal increases; d) as a first input; Input the voltage between the output terminals of the variable output impedance, input the voltage between the input terminals of the voltage follower circuit as a second input, and input the voltage difference between the first input and the second input to the input terminal of the variable impedance. A power control system comprising: voltage detection means for supplying a representative output voltage signal.